The broad, long-term goals of the proposed study are to determine the prevalence and natural history of tracheomalacia among patients with chronic obstructive pulmonary disease (COPD) and to establish the role of a novel CT method in guiding therapy and assessing response to intervention. This work also has the potential to reduce morbidity among patients with coexisting COPD and tracheomalacia. Chronic cough is the fifth most common symptom for which patients seek medical care in the United States, accounting for more than 30 million office visits per year. Acquired tracheomalacia, a condition defined by excessive expiratory collapse of the trachea due to weakness of the airway walls and/or supporting cartilage, is a relatively common but frequently overlooked cause of chronic cough. Tracheomalacia is associated with a variety of risk factors, most notably COPD. Importantly, tracheomalacia can cause significant respiratory morbidity if left untreated, and it may rarely be fatal. Our preliminary studies demonstrate that paired inspiratory-dynamic expiratory CT is a highly accurate, noninvasive method for diagnosing tracheomalacia, with comparable accuracy to the current gold standard of bronchoscopy, an invasive procedure. We propose a diagnostic study which will be a collaborative, multidisciplinary effort by the departments of radiology, pulmonary medicine, thoracic surgery, pathology, and anesthesia at Beth Israel Deaconess Medical Center and Harvard Medical School, a center that has established expertise in the diagnosis and treatment of this disorder. We propose the following specific aims: Aim 1: Determine the prevalence of tracheomalacia among patients with COPD; Aim 2: Identify physiological and clinical parameters that are predictive of tracheomalacia in patients with COPD; Aim 3: Determine the natural history of tracheomalacia in the absence of intervention among subjects who are asymptomatic or mildly symptomatic; and Aim 4: Identify factors that are predictive of a positive response to intervention by assessing longitudinal changes in key parameters among severely symptomatic participants following therapy. The import of the proposed study is two-fold: 1) it will noninvasively determine the prevalence and natural history of tracheomalacia among patients with COPD; and 2) it has the potential to reduce morbidity among patients with coexisting COPD and tracheomalacia. Narrative: Acquired tracheomalacia, a condition defined by excessive expiratory collapse of the trachea due to weakness of the airway walls and/or supporting cartilage, is a common but often overlooked cause of chronic respiratory symptoms that is associated with a variety of risk factors, most notably chronic obstructive pulmonary disease (COPD). The broad, long-term goals of the proposed study are to determine the prevalence and natural history of tracheomalacia among patients with COPD and to establish the role of a novel CT method in guiding therapy and assessing response to intervention. This work also has the potential to reduce morbidity among patients with coexisting COPD and tracheomalacia.